The present invention relates to an impeller wheel for conveying a medium of the type including a plurality of vanes spaced from each other.
The effect of a non-uniform distribution of intervals between the vanes of the impeller on the noise generation is determined in a frequency range. With a uniform distribution of vanes in the impeller a tone or a sound with frequency N f.sub.o and high harmonics thereof are produced wherein N is the number of vanes and f.sub.o is the rotation frequency of the impeller wheel. Without taking into consideration the uppertone the intensity/frequency spectrum of this noise consists of a discrete line which indicates the entire sound energy (FIG. 1a). The purpose of the non-uniform or irregular vane distribution is that the sound intensity of the single spectrum line be uniformly subdivided into many discrete lines in the frequency range so that each partial tone would be below the audible threshold of hearing.
An impeller has been known from DE-AS 1253402, in which the instructions have been given as to how the vane positions should be distributed on the periphery of the impeller wheel. Thereby a mathematical equation between the succession of the intervals between the vanes and the resulting noise spectrum has not been considered so that, for example the subdivision of the output spectrum can develop as shown in FIG. 1b, in which individual tones dominate. The degree of irregularity for a given successions of the vane intervals is defined in that the difference between the maximal and minimal interval is divided by the middle interval. This definition does not take into consideration the succession of different intervals which are very important for the aforementioned irregularity.